Not Applicable
Not Applicable
A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever.
1. Field of the Invention
This invention pertains generally to companding amplifiers, and more particularly to a companding amplifier where expansion gain is digitally controlled over a sidechannel.
2. Description of the Background Art
Companding amplifiers are well known in the art, and an example of a conventional companding amplifier can be found in U.S. Pat. No. 5,473,279 which is incorporated herein by reference. Conventional companding amplifiers typically employ circuitry that compresses an audio input signal using a full wave rectifier and peak detector or their equivalent. An expanding amplifier then uses the peak to peak amplitude as a metric for the amount of expansion.
While conventional companding amplifiers are suitable for voice communication, the are not suitable for transmission of music. Due to the lag time of expansion, in conventional companding amplifiers you can hear the compression in the music before the expander has time to react. If the compression expander timing is shortened, the THD becomes unbearable. Accordingly, current companding amplifier technology does not effectively use the dynamic range of he communication channel. The expansion amount is determined by the level of the signal, and the full channel bandwidth cannot be used all of the time.
In addition, analog to digital converters used in conventional companding amplifiers have problems with the accommodation of small signals and very large signals. If the converter is set to accommodate large signals during loud passages of music, quiet passages presented to the converter may be lost in the noise floor of the converter. If the A/D converter is set for small signals, then clipping will occur during loud passages of music.
Therefore, there is a need for a companding amplifier that will effectively extend the dynamic range of analog to digital converters and provide for transmission of music.
The present invention satisfies those needs, as well as others, and overcomes the deficiencies found in companding amplifiers previously developed.
The present invention comprises a companding amplifier wherein compression data is provided to an expander along with audio data. By way of example, and not of limitation, the invention includes a voltage controlled amplifier (compressor), a data framer, a data separator, a voltage controlled attenuator (expander), and both analog to digital and digital to analog converters. An audio input signal is compressed by the compressor and converted into digital data. Compression and data framing is controlled by a microprocessor that provides both compression signals to the voltage controlled amplifier and digital compression data to the data framer. The data framer produces a digital data stream that contains both the digital audio data and the digital compression data. The resultant digital data stream can then be recorded on a medium such as a CD or DAT, or transmitted over a medium such as wire, fiber optic or radio waves. Prior to expansion, the data separator separates the digital audio data and digital compression data. The digital audio data is then converted back to an analog audio signal and presented to the voltage controlled attenuator, and the digital compression data is converted to an analog control signal and used as the control signal for the voltage controlled attenuator amplifier. The xe2x80x9csidechannelxe2x80x9d control of the expansion circuit with separate gain data results in an increase in dynamic range.
An object of the invention is to increase the dynamic range of a companding amplifier.
Another object of the invention is to separate gain data from audio data in a companding amplifier.
Another object of the invention to present gain data to an expander that is separate from the audio data.
Another object of the invention is to send digital gain data with digital audio data for reconstruction of a compressed audio signal by an expander.
Another object of the invention is to send gain data to an expander for control expansion level.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.